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Linux/mm/mremap.c

  1 /*
  2  *      mm/mremap.c
  3  *
  4  *      (C) Copyright 1996 Linus Torvalds
  5  *
  6  *      Address space accounting code   <alan@lxorguk.ukuu.org.uk>
  7  *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
  8  */
  9 
 10 #include <linux/mm.h>
 11 #include <linux/hugetlb.h>
 12 #include <linux/shm.h>
 13 #include <linux/ksm.h>
 14 #include <linux/mman.h>
 15 #include <linux/swap.h>
 16 #include <linux/capability.h>
 17 #include <linux/fs.h>
 18 #include <linux/swapops.h>
 19 #include <linux/highmem.h>
 20 #include <linux/security.h>
 21 #include <linux/syscalls.h>
 22 #include <linux/mmu_notifier.h>
 23 #include <linux/uaccess.h>
 24 #include <linux/mm-arch-hooks.h>
 25 
 26 #include <asm/cacheflush.h>
 27 #include <asm/tlbflush.h>
 28 
 29 #include "internal.h"
 30 
 31 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
 32 {
 33         pgd_t *pgd;
 34         pud_t *pud;
 35         pmd_t *pmd;
 36 
 37         pgd = pgd_offset(mm, addr);
 38         if (pgd_none_or_clear_bad(pgd))
 39                 return NULL;
 40 
 41         pud = pud_offset(pgd, addr);
 42         if (pud_none_or_clear_bad(pud))
 43                 return NULL;
 44 
 45         pmd = pmd_offset(pud, addr);
 46         if (pmd_none(*pmd))
 47                 return NULL;
 48 
 49         return pmd;
 50 }
 51 
 52 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
 53                             unsigned long addr)
 54 {
 55         pgd_t *pgd;
 56         pud_t *pud;
 57         pmd_t *pmd;
 58 
 59         pgd = pgd_offset(mm, addr);
 60         pud = pud_alloc(mm, pgd, addr);
 61         if (!pud)
 62                 return NULL;
 63 
 64         pmd = pmd_alloc(mm, pud, addr);
 65         if (!pmd)
 66                 return NULL;
 67 
 68         VM_BUG_ON(pmd_trans_huge(*pmd));
 69 
 70         return pmd;
 71 }
 72 
 73 static void take_rmap_locks(struct vm_area_struct *vma)
 74 {
 75         if (vma->vm_file)
 76                 i_mmap_lock_write(vma->vm_file->f_mapping);
 77         if (vma->anon_vma)
 78                 anon_vma_lock_write(vma->anon_vma);
 79 }
 80 
 81 static void drop_rmap_locks(struct vm_area_struct *vma)
 82 {
 83         if (vma->anon_vma)
 84                 anon_vma_unlock_write(vma->anon_vma);
 85         if (vma->vm_file)
 86                 i_mmap_unlock_write(vma->vm_file->f_mapping);
 87 }
 88 
 89 static pte_t move_soft_dirty_pte(pte_t pte)
 90 {
 91         /*
 92          * Set soft dirty bit so we can notice
 93          * in userspace the ptes were moved.
 94          */
 95 #ifdef CONFIG_MEM_SOFT_DIRTY
 96         if (pte_present(pte))
 97                 pte = pte_mksoft_dirty(pte);
 98         else if (is_swap_pte(pte))
 99                 pte = pte_swp_mksoft_dirty(pte);
100 #endif
101         return pte;
102 }
103 
104 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
105                 unsigned long old_addr, unsigned long old_end,
106                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
107                 unsigned long new_addr, bool need_rmap_locks)
108 {
109         struct mm_struct *mm = vma->vm_mm;
110         pte_t *old_pte, *new_pte, pte;
111         spinlock_t *old_ptl, *new_ptl;
112 
113         /*
114          * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
115          * locks to ensure that rmap will always observe either the old or the
116          * new ptes. This is the easiest way to avoid races with
117          * truncate_pagecache(), page migration, etc...
118          *
119          * When need_rmap_locks is false, we use other ways to avoid
120          * such races:
121          *
122          * - During exec() shift_arg_pages(), we use a specially tagged vma
123          *   which rmap call sites look for using is_vma_temporary_stack().
124          *
125          * - During mremap(), new_vma is often known to be placed after vma
126          *   in rmap traversal order. This ensures rmap will always observe
127          *   either the old pte, or the new pte, or both (the page table locks
128          *   serialize access to individual ptes, but only rmap traversal
129          *   order guarantees that we won't miss both the old and new ptes).
130          */
131         if (need_rmap_locks)
132                 take_rmap_locks(vma);
133 
134         /*
135          * We don't have to worry about the ordering of src and dst
136          * pte locks because exclusive mmap_sem prevents deadlock.
137          */
138         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
139         new_pte = pte_offset_map(new_pmd, new_addr);
140         new_ptl = pte_lockptr(mm, new_pmd);
141         if (new_ptl != old_ptl)
142                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
143         arch_enter_lazy_mmu_mode();
144 
145         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
146                                    new_pte++, new_addr += PAGE_SIZE) {
147                 if (pte_none(*old_pte))
148                         continue;
149                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
150                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
151                 pte = move_soft_dirty_pte(pte);
152                 set_pte_at(mm, new_addr, new_pte, pte);
153         }
154 
155         arch_leave_lazy_mmu_mode();
156         if (new_ptl != old_ptl)
157                 spin_unlock(new_ptl);
158         pte_unmap(new_pte - 1);
159         pte_unmap_unlock(old_pte - 1, old_ptl);
160         if (need_rmap_locks)
161                 drop_rmap_locks(vma);
162 }
163 
164 #define LATENCY_LIMIT   (64 * PAGE_SIZE)
165 
166 unsigned long move_page_tables(struct vm_area_struct *vma,
167                 unsigned long old_addr, struct vm_area_struct *new_vma,
168                 unsigned long new_addr, unsigned long len,
169                 bool need_rmap_locks)
170 {
171         unsigned long extent, next, old_end;
172         pmd_t *old_pmd, *new_pmd;
173         bool need_flush = false;
174         unsigned long mmun_start;       /* For mmu_notifiers */
175         unsigned long mmun_end;         /* For mmu_notifiers */
176 
177         old_end = old_addr + len;
178         flush_cache_range(vma, old_addr, old_end);
179 
180         mmun_start = old_addr;
181         mmun_end   = old_end;
182         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
183 
184         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
185                 cond_resched();
186                 next = (old_addr + PMD_SIZE) & PMD_MASK;
187                 /* even if next overflowed, extent below will be ok */
188                 extent = next - old_addr;
189                 if (extent > old_end - old_addr)
190                         extent = old_end - old_addr;
191                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
192                 if (!old_pmd)
193                         continue;
194                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
195                 if (!new_pmd)
196                         break;
197                 if (pmd_trans_huge(*old_pmd)) {
198                         if (extent == HPAGE_PMD_SIZE) {
199                                 bool moved;
200                                 /* See comment in move_ptes() */
201                                 if (need_rmap_locks)
202                                         take_rmap_locks(vma);
203                                 moved = move_huge_pmd(vma, old_addr, new_addr,
204                                                     old_end, old_pmd, new_pmd);
205                                 if (need_rmap_locks)
206                                         drop_rmap_locks(vma);
207                                 if (moved) {
208                                         need_flush = true;
209                                         continue;
210                                 }
211                         }
212                         split_huge_pmd(vma, old_pmd, old_addr);
213                         if (pmd_none(*old_pmd))
214                                 continue;
215                         VM_BUG_ON(pmd_trans_huge(*old_pmd));
216                 }
217                 if (pte_alloc(new_vma->vm_mm, new_pmd, new_addr))
218                         break;
219                 next = (new_addr + PMD_SIZE) & PMD_MASK;
220                 if (extent > next - new_addr)
221                         extent = next - new_addr;
222                 if (extent > LATENCY_LIMIT)
223                         extent = LATENCY_LIMIT;
224                 move_ptes(vma, old_pmd, old_addr, old_addr + extent,
225                           new_vma, new_pmd, new_addr, need_rmap_locks);
226                 need_flush = true;
227         }
228         if (likely(need_flush))
229                 flush_tlb_range(vma, old_end-len, old_addr);
230 
231         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
232 
233         return len + old_addr - old_end;        /* how much done */
234 }
235 
236 static unsigned long move_vma(struct vm_area_struct *vma,
237                 unsigned long old_addr, unsigned long old_len,
238                 unsigned long new_len, unsigned long new_addr, bool *locked)
239 {
240         struct mm_struct *mm = vma->vm_mm;
241         struct vm_area_struct *new_vma;
242         unsigned long vm_flags = vma->vm_flags;
243         unsigned long new_pgoff;
244         unsigned long moved_len;
245         unsigned long excess = 0;
246         unsigned long hiwater_vm;
247         int split = 0;
248         int err;
249         bool need_rmap_locks;
250 
251         /*
252          * We'd prefer to avoid failure later on in do_munmap:
253          * which may split one vma into three before unmapping.
254          */
255         if (mm->map_count >= sysctl_max_map_count - 3)
256                 return -ENOMEM;
257 
258         /*
259          * Advise KSM to break any KSM pages in the area to be moved:
260          * it would be confusing if they were to turn up at the new
261          * location, where they happen to coincide with different KSM
262          * pages recently unmapped.  But leave vma->vm_flags as it was,
263          * so KSM can come around to merge on vma and new_vma afterwards.
264          */
265         err = ksm_madvise(vma, old_addr, old_addr + old_len,
266                                                 MADV_UNMERGEABLE, &vm_flags);
267         if (err)
268                 return err;
269 
270         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
271         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
272                            &need_rmap_locks);
273         if (!new_vma)
274                 return -ENOMEM;
275 
276         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
277                                      need_rmap_locks);
278         if (moved_len < old_len) {
279                 err = -ENOMEM;
280         } else if (vma->vm_ops && vma->vm_ops->mremap) {
281                 err = vma->vm_ops->mremap(new_vma);
282         }
283 
284         if (unlikely(err)) {
285                 /*
286                  * On error, move entries back from new area to old,
287                  * which will succeed since page tables still there,
288                  * and then proceed to unmap new area instead of old.
289                  */
290                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
291                                  true);
292                 vma = new_vma;
293                 old_len = new_len;
294                 old_addr = new_addr;
295                 new_addr = err;
296         } else {
297                 arch_remap(mm, old_addr, old_addr + old_len,
298                            new_addr, new_addr + new_len);
299         }
300 
301         /* Conceal VM_ACCOUNT so old reservation is not undone */
302         if (vm_flags & VM_ACCOUNT) {
303                 vma->vm_flags &= ~VM_ACCOUNT;
304                 excess = vma->vm_end - vma->vm_start - old_len;
305                 if (old_addr > vma->vm_start &&
306                     old_addr + old_len < vma->vm_end)
307                         split = 1;
308         }
309 
310         /*
311          * If we failed to move page tables we still do total_vm increment
312          * since do_munmap() will decrement it by old_len == new_len.
313          *
314          * Since total_vm is about to be raised artificially high for a
315          * moment, we need to restore high watermark afterwards: if stats
316          * are taken meanwhile, total_vm and hiwater_vm appear too high.
317          * If this were a serious issue, we'd add a flag to do_munmap().
318          */
319         hiwater_vm = mm->hiwater_vm;
320         vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
321 
322         /* Tell pfnmap has moved from this vma */
323         if (unlikely(vma->vm_flags & VM_PFNMAP))
324                 untrack_pfn_moved(vma);
325 
326         if (do_munmap(mm, old_addr, old_len) < 0) {
327                 /* OOM: unable to split vma, just get accounts right */
328                 vm_unacct_memory(excess >> PAGE_SHIFT);
329                 excess = 0;
330         }
331         mm->hiwater_vm = hiwater_vm;
332 
333         /* Restore VM_ACCOUNT if one or two pieces of vma left */
334         if (excess) {
335                 vma->vm_flags |= VM_ACCOUNT;
336                 if (split)
337                         vma->vm_next->vm_flags |= VM_ACCOUNT;
338         }
339 
340         if (vm_flags & VM_LOCKED) {
341                 mm->locked_vm += new_len >> PAGE_SHIFT;
342                 *locked = true;
343         }
344 
345         return new_addr;
346 }
347 
348 static struct vm_area_struct *vma_to_resize(unsigned long addr,
349         unsigned long old_len, unsigned long new_len, unsigned long *p)
350 {
351         struct mm_struct *mm = current->mm;
352         struct vm_area_struct *vma = find_vma(mm, addr);
353         unsigned long pgoff;
354 
355         if (!vma || vma->vm_start > addr)
356                 return ERR_PTR(-EFAULT);
357 
358         if (is_vm_hugetlb_page(vma))
359                 return ERR_PTR(-EINVAL);
360 
361         /* We can't remap across vm area boundaries */
362         if (old_len > vma->vm_end - addr)
363                 return ERR_PTR(-EFAULT);
364 
365         if (new_len == old_len)
366                 return vma;
367 
368         /* Need to be careful about a growing mapping */
369         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
370         pgoff += vma->vm_pgoff;
371         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
372                 return ERR_PTR(-EINVAL);
373 
374         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
375                 return ERR_PTR(-EFAULT);
376 
377         if (vma->vm_flags & VM_LOCKED) {
378                 unsigned long locked, lock_limit;
379                 locked = mm->locked_vm << PAGE_SHIFT;
380                 lock_limit = rlimit(RLIMIT_MEMLOCK);
381                 locked += new_len - old_len;
382                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
383                         return ERR_PTR(-EAGAIN);
384         }
385 
386         if (!may_expand_vm(mm, vma->vm_flags,
387                                 (new_len - old_len) >> PAGE_SHIFT))
388                 return ERR_PTR(-ENOMEM);
389 
390         if (vma->vm_flags & VM_ACCOUNT) {
391                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
392                 if (security_vm_enough_memory_mm(mm, charged))
393                         return ERR_PTR(-ENOMEM);
394                 *p = charged;
395         }
396 
397         return vma;
398 }
399 
400 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
401                 unsigned long new_addr, unsigned long new_len, bool *locked)
402 {
403         struct mm_struct *mm = current->mm;
404         struct vm_area_struct *vma;
405         unsigned long ret = -EINVAL;
406         unsigned long charged = 0;
407         unsigned long map_flags;
408 
409         if (offset_in_page(new_addr))
410                 goto out;
411 
412         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
413                 goto out;
414 
415         /* Ensure the old/new locations do not overlap */
416         if (addr + old_len > new_addr && new_addr + new_len > addr)
417                 goto out;
418 
419         ret = do_munmap(mm, new_addr, new_len);
420         if (ret)
421                 goto out;
422 
423         if (old_len >= new_len) {
424                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
425                 if (ret && old_len != new_len)
426                         goto out;
427                 old_len = new_len;
428         }
429 
430         vma = vma_to_resize(addr, old_len, new_len, &charged);
431         if (IS_ERR(vma)) {
432                 ret = PTR_ERR(vma);
433                 goto out;
434         }
435 
436         map_flags = MAP_FIXED;
437         if (vma->vm_flags & VM_MAYSHARE)
438                 map_flags |= MAP_SHARED;
439 
440         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
441                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
442                                 map_flags);
443         if (offset_in_page(ret))
444                 goto out1;
445 
446         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
447         if (!(offset_in_page(ret)))
448                 goto out;
449 out1:
450         vm_unacct_memory(charged);
451 
452 out:
453         return ret;
454 }
455 
456 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
457 {
458         unsigned long end = vma->vm_end + delta;
459         if (end < vma->vm_end) /* overflow */
460                 return 0;
461         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
462                 return 0;
463         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
464                               0, MAP_FIXED) & ~PAGE_MASK)
465                 return 0;
466         return 1;
467 }
468 
469 /*
470  * Expand (or shrink) an existing mapping, potentially moving it at the
471  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
472  *
473  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
474  * This option implies MREMAP_MAYMOVE.
475  */
476 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
477                 unsigned long, new_len, unsigned long, flags,
478                 unsigned long, new_addr)
479 {
480         struct mm_struct *mm = current->mm;
481         struct vm_area_struct *vma;
482         unsigned long ret = -EINVAL;
483         unsigned long charged = 0;
484         bool locked = false;
485 
486         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
487                 return ret;
488 
489         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
490                 return ret;
491 
492         if (offset_in_page(addr))
493                 return ret;
494 
495         old_len = PAGE_ALIGN(old_len);
496         new_len = PAGE_ALIGN(new_len);
497 
498         /*
499          * We allow a zero old-len as a special case
500          * for DOS-emu "duplicate shm area" thing. But
501          * a zero new-len is nonsensical.
502          */
503         if (!new_len)
504                 return ret;
505 
506         if (down_write_killable(&current->mm->mmap_sem))
507                 return -EINTR;
508 
509         if (flags & MREMAP_FIXED) {
510                 ret = mremap_to(addr, old_len, new_addr, new_len,
511                                 &locked);
512                 goto out;
513         }
514 
515         /*
516          * Always allow a shrinking remap: that just unmaps
517          * the unnecessary pages..
518          * do_munmap does all the needed commit accounting
519          */
520         if (old_len >= new_len) {
521                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
522                 if (ret && old_len != new_len)
523                         goto out;
524                 ret = addr;
525                 goto out;
526         }
527 
528         /*
529          * Ok, we need to grow..
530          */
531         vma = vma_to_resize(addr, old_len, new_len, &charged);
532         if (IS_ERR(vma)) {
533                 ret = PTR_ERR(vma);
534                 goto out;
535         }
536 
537         /* old_len exactly to the end of the area..
538          */
539         if (old_len == vma->vm_end - addr) {
540                 /* can we just expand the current mapping? */
541                 if (vma_expandable(vma, new_len - old_len)) {
542                         int pages = (new_len - old_len) >> PAGE_SHIFT;
543 
544                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
545                                        vma->vm_pgoff, NULL)) {
546                                 ret = -ENOMEM;
547                                 goto out;
548                         }
549 
550                         vm_stat_account(mm, vma->vm_flags, pages);
551                         if (vma->vm_flags & VM_LOCKED) {
552                                 mm->locked_vm += pages;
553                                 locked = true;
554                                 new_addr = addr;
555                         }
556                         ret = addr;
557                         goto out;
558                 }
559         }
560 
561         /*
562          * We weren't able to just expand or shrink the area,
563          * we need to create a new one and move it..
564          */
565         ret = -ENOMEM;
566         if (flags & MREMAP_MAYMOVE) {
567                 unsigned long map_flags = 0;
568                 if (vma->vm_flags & VM_MAYSHARE)
569                         map_flags |= MAP_SHARED;
570 
571                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
572                                         vma->vm_pgoff +
573                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
574                                         map_flags);
575                 if (offset_in_page(new_addr)) {
576                         ret = new_addr;
577                         goto out;
578                 }
579 
580                 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
581         }
582 out:
583         if (offset_in_page(ret)) {
584                 vm_unacct_memory(charged);
585                 locked = 0;
586         }
587         up_write(&current->mm->mmap_sem);
588         if (locked && new_len > old_len)
589                 mm_populate(new_addr + old_len, new_len - old_len);
590         return ret;
591 }
592 

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